Cooling means for aircraft engine exhaust stacks



April 23, 1940. N. c. PRICE 2,198,229

COOLING MEANS FOR AIRCRAFT ENGINE EXHAUST STACKS Filed July 16, 1937Snnentor NOIH'JOII] C Price attorney Patented Apr. 23, 1940 PATENTOFFICE COOLING DIEANS FOR. AIRCRAFT ENGINE EXHAUST STACKS bankingassociation Application July 16, 1937, Serial No. 153,972 Claims. 01.244-53) My invention relates to the cooling of the ex-' haust stack ofairplane engines. The cooling of airplane exhausts has long been aproblem to aircraft designers, Heretofore the exhaust a stack has beencarried out of the engine nacelle as soon as possible to get it out intothe air stream. This was deemed necessary by designers owing to theintense heat of the exhaust stack. The streamlining of portance.Obviously, then, running an exhaust stack into theair stream for anydistance reduces the effectiveness of the streamlining. To relieve thissituation the exhaust stack was placed within the nacelle and wasenclosed in a sleeve. This sleeve was, at its forward end, projectedinto the air stream in the form of a ram, or scoop, and thus the air wasforced into this scoop, located in the air stream, thence carried up tothe part of the sleeve surrounding the exhaust stack, and then along thestack until it was again projected into the air stream along with theexhaust gases. This system worked very well in theory but in actualpractice a new difficulty was experienced, that of having ice forming inthe intake scoop and restricting the amount of air passing around theexhaust stack, many times closing the air intake entirely. Thus, withthis type of cooling and after the formation of ice in the intake, therewas no longer any cooling, and the heat from the exhaust became arealsource of danger;

Other ideas have been advanced which would provide sufli'cient coolingfor the exhaust stack with little added wind resistance and stillprevent the formation of icethat interferes with the cooling system-IThe main principle embodied in these ideas was the recessing of theexhaust stack in the engine nacelle, still keeping it outside to providesufficient air for cooling. Therecessing of the engine nacelle resultedin a weakening of that structure. To compensate for this generalweakening additional structural members, or heavier and strongermembers, would have to be added. Dead weight-is another factor extremelyimportant in airplane design and the addition of structural members, orthe use of heavier members, would necessarily increase the dead load ofthe airplane.

The object of my invention is to provide a. means of cooling the exhauststacks of airplane motors which is free from all the difficultiesheretofore described.

In the accompanying drawing my invention is shown embodied in a formwhich last present ll preferred by me.

airplanes is of prime im-,

Figure 1 is in part an elevation and in part a section through thecomplete device, as assembled in the engine nacelle.

Figure 2 is an enlarged section of the device itself, showing the methodof mounting the exhaust stack in the cooling sleeve.

The exhaust stack I extends rearwardly from the collector ring H], asusual, but is enclosed within the nacelle skin or cowling 2, in suchmanner as will not interfere with the latter nor with the structuralmembers of the usual engine rnount or of the nacelle. It is alsoentirely within the cowl ring 3. If a fire wall is provided, as iscustomary, and as is illustrated at 20, the exhaust stack I extendsthrough this fire Wall, and terminates at or near the skin of thenacelle. Such an arrangement does not differ essentially from formerarrangements wherein a rammed air supply cools the stack, but thepresent arrangement differs from the latter in providing means otherthan the force of the air at the entrance of a ram or scoop to move thecooling air lengthwise of the stack.

To concentrate the cooling air in'the vicinity of the stack I, it issurrounded by a sleeve 4, the entrance 40 of which islocated within thecowl ring 3, but within a space wherein is available a continuous airsupply, preferably under some Thus, the entrance 40 may be in or inadvance of the fire wall 20, and inrear of the engine cylinders (notshown). In this region air which has entered the central nose opening ofthe pressure.

cowl ring 3, and which has passed and cooled the engine cylinders, isavailable under some pressure, and while it has been warmed, it is farbelow the temperature of the exhaust gases, and can keep the stack lcool, particularly as large volumes of air are moved rapidly through thesleeve.

The sleeve 4 is spaced from the exhaust stack, throughout its length, bysuitablespacers, as H. Exclusive reliance is not placed upon thepressure at the entrance an to force the air through the sleeve, butauxiliary means are provided at the exit 42 of the sleeve to induce aflow of air through the sleeve, and hence over the stack l. Variousmeans to this end may be employed, but one of the most satisfactorymeans is to provide, in the sleeve, a venturi 43 so placed with respectto the outlet l3 of the stack, that the exhaust pressure from the stackwill operate, by jet action, to induce a draft oi air through thesleeve.

In addition, if the outlet 42 of the venturi and sleeve is projectedthrough the nacelle skin 2 in a low pressure area, or is beveled in suchmanner, with respect to the relative airflow, as to produce a suction, afurther or additive suction eifect is produced, further assisting indrawing air through the sleeve.

There is nothing projecting into the air stream, in this arrangement,except the terminus 421 of the sleeve, and this causes no material drag,and no material weakening of the nacelle. The air which enters thesleeve at 40 is never subjected to icing conditions, and in fact hasbeen preliminarily heated somewhat. It has been found that thisarrangement will lower the temperature of the exhaust stack, in atypical installation, by about 1000 F., and hence maintains amplecooling. v

What I claim as my invention is:

1. In combination with the ring cowl of an aircraft engine and with theexhaust stack, an aircraft structure supporting the ring' cowl, andwholly enclosing the exhaust stack, a sleeve within the aircraftstructure, surrounding said stack, the rear end of said sleeveprojecting a substantial distance out into the atmosphere, and beingrearwardly directed, its forward end opening within the ring cowl to aspace filled with air under a pressure higher than that of the ambientatmosphere, whereby to induce a flow of air through said sleeve, and aVenturi throat formed in the rear end of the sleeve, the rear end of theexhaust stack discharging into said Venturi throat, thereby to enhancethe flow of air through the sleeve.

2. In combination with a ring cowl for a radial air-cooled aircraftengine, an aircraft structure supporting the several parts and whollyenclosing an exhaust stack, a sleeve surrounding but spaced from theexhaust stack and open at its forward end within the ring cowl for theadmission of air, a Venturi throat formed at the rear end of said sleeveand said sleeve projecting through and beyond an opening in the aircraftstructure, and so disposed with relation to the end of the stack thatthe discharge of exhaust gases from the latter will induce a flow of airthrough the sleeve.

3. In combination with anaircraft structure such as an engine nacelle,and with the exhaust stack of an airplane engine, extending through suchaircraft structure, said stack being circular in cross section, acylindrical sleeve wholly enclosed within the aircraft structure, andclosely encompassing said stack along its length but spaced from it andclosely conforming to the stack in shape from one end to the other endthereof, an air inletopening adjacent the en- 'gine for admission of airto said sleeve, a venturi surrounding the discharge and of said stack,open at one end to the atmosphere, and having its axis disposed at anangle -,to the direction of motion of the relative air stream sweepingpast such open end, and at its other end comm-uni? cating with said'sleeve,-,- and so arranged, rela-.

' tive to such discharge end of the. stack, that the jet action ofexhaust gases discharged from the stack induces air flow at a relativelyhigh velocity through said member and over the stack, and a diffuserleading from venturi;and ,proiecting a substantial distance out intosaidistream.

4, Mechanism as in claim '3, and further characterizedzby said diffuserbeing beveled lat'its outlet so that the leading edge of the outletextends further into the stream than the trailing edge. 5. Incombination with a ring cowl, surroundan exhaust through the" partitionto discharge to the atmosphere, and a sleeve surrounding and spaced fromthe exhaust'stack, its intake end opening adjacent to the engine to airpressure in'excess of atmospheric'built up within the ring cowl forwardof the partition, sleeve extending beyond the discharge end of saidexhaust stack and projecting a substantial distance out into theatmosphere beyond .an opening in the aircraft structure, and beingbeveledso that'the leading edge of the outlet end extends farther intothe air stream than the trailing edge thereof,-for operation as an aireductor accelerating discharge from said sleeve.

mm 0. PRICE.

ing an airplane engine, open to the front and closed at the rear by apartition,

stack connected to the engine and extending and the outlet end of said

